FIG. 1 schematically illustrates a WCDMA RAN that generally comprises one or more radio network controllers (RNC) 110 and Radio Base Stations (RBSs) 120a,b. The RNC 110 is connected via cables to the core network 105 and to the RBSs 120a, 120b. The RBSs 120 are adapted to communicate wirelessly with user equipments (UEs) 130a-d, also referred to as mobile terminals over the radio interface.
Two types of testing will be considered in the following: stability/performance/resource testing of a WCDMA RAN and WCDMA cell capacity testing. The aim of stability/performance/resource testing of the WCDMA RAN is to verify the stability and performance and resource usage of the WCMDA RAN. This implies that the interaction between different resource handling algorithms and radio algorithms are tested with real traffic at high traffic load levels. Cell Capacity testing implies testing of cell capacity with load generated by many concurrent users within the cell. The purpose of this testing is to verify cell capacity against theoretical requirements and to identify performance limits, for example increase of uplink interference versus traffic load.
Laboratory testing of a WCMDA RAN is performed in an environment consisting of a number of RBSs, whereby each RBS has one or more cells as shown in FIG. 2 illustrating the physical layout. These RBSs 201-204 are controlled by the RNC 200 which is attached to the core network. Traffic is generated in the radio cells by real mobile terminals (UEs). The cells and the UEs are connected via a Closed Cellular Network (CCN) which provides mobility over cell boarders for the attached UEs. Hence, the CCN 206 is variable attenuation system comprising of a coaxial network. The CCN 206 simulates UE mobility and it is possible to define a drive route. The mobility simulations of the CCN 206 are able to consider interference but fading is not taken into account. The corresponding logical layout is illustrated in FIG. 3.
The UEs are arranged in UE-groups 207-210, wherein all UEs within in a UE-group are connected to all cells (only cell and cell 2 of RBS 1 are indicated in FIG. 2) within the radio network and the UEs perform cell selection to identify best serving cell within the network. Each group consists of typical 8-14 UEs. For each UE-group a drive route 211, 212 through the CCN could be defined. with the purpose of testing the RAN in terms of a number of key performance indicators such as call setup success rates, drop rates, handover success rates et cetera.
Laboratory testing of WCDMA cell capacity is currently made in an RF-chamber with 1 up to 50 UEs attached to a cell via coaxial cables. Requirements related to cell capacity include specifications of radio conditions valid for the requirement, such as non-fading or fading of the radio channel. As an example, a requirement could state that the uplink interference shall not increase more than y dB with x simultaneous speech users in the cell with a radio channel according to TU3 (Typical Urban 3 km/h, standardized channel model with fading).
When fading is required, the fading is typical generated with channel emulators, where each of the currently used emulators could handle e.g. three radio channels. Hence a UE with uplink and downlink fading plus uplink diversity would require 3 channels i.e. one channel emulator per UE.
For the WCDMA cell capacity testing, it would be difficult to provide independent fading for all UEs when the number of required UEs outnumbers the available channel emulators due to cost as well as practical reasons. When that is the case, more than one UE has to share the same channel emulator resource. The lack of independent fading will cause too high correlation between UEs on the same channel emulator. This in turn would cause the power regulation to increase the power to too high levels causing too high interference in the cell.
Also for the Stability/performance/resource testing of WCDMA RAN, the current solution does not provide a realistic radio environment since coaxial cables are used to connect UEs to the RAN. As stated above, the normal way to introduce fading in a lab environment (i.e. connection via coaxial cables) is to insert a channel emulator in between the UE and the RBS which implies the drawbacks as mentioned above. Thus, simulation of fading by using channel emulators require too many emulators and additionally the performance is not good enough. This means that fading which an important characteristic of the radio environment can not be taken into account by the current solution.
Without fading important properties of RAN like power control and resource handling cannot be tested thoroughly.